In the second year of this grant the work was focussed on the uridine pathway and the role of uridine kinase in the control of RNA metabolism. The uridine kinase that exists in the majority of eukaryotes is allosterically inhibited by UTP and CTP. On the contrary, the uridine kinase that exists in A364A with Z164-8D behaved like Z164-8D parental strain in which the uridine kinase is highly sensitive to feedback inhibition by the ribonucleoside triphosphate. A new method of purification of the A364A uridine kinase, which is resistant to allosteric inhibition by UTP, was developed since this enzyme is activated by any compound which contains a SO4 double negative ion group. The method consists in protamine chloride precipitation followed by acetic acid precipitation. A 200-fold purification is achieved after absorbtion to a carboxylmethyl cellulose column and elution at pH 6.0 with a salt gradient. Physiological and genetic evidence supports the concept that in the majority of eukaryotes there is no coordination between the RNA polymerase and uridine kinase activities. This indicates that changes in the amount of radioactive uridine incorporated into RNA can occur with no changes in the rate of polymerization of ribonucleotide chains or number of growing chains. Conversely, it is also possible to have changes in the number of growing RNA chains or in the rate of polymerization of these changes with equal amounts of labelled uridine incorporated into RNA. BIBLIOGRAPHIC REFERENCES: Hanna Chroboczek Kelker, Kurt J. Gross and A.O. Pogo (1977) Effect of Amino Acid Starvation and Addition of Cycloheximide on the Rate of H-Uridine Incorporation into Yeast RNA species. Fed. Proc., in press. Amer. Soc Biol. Chem. Meeting, Chicago. K. J. Gross, A.O. Pogo and M.S. Esposito (1977) RNA Polymerase and Uridine Kinase Interaction: The Effect of Stimulation and Inhibition of RNA Synthesis. Fed. Proc., in press. Amer. Soc. Biol. Chem. Meeting, Chicago.